Do question 7 and 9 in a page

Dear student, 
7. Time taken by sound to reach the observer:  5sec
     speed of sound in air: 330 m/s
     distance travelled : speed x time
                                    = 330x 5 = 1650 m
9.
Let the speed of sound in air be v. 
so the distance between the two tanks will be speed x time difference between them. 



Regards.